1. Field of the Invention
This invention relates to a pneumatically operated double acting pump especially suited for pumping viscous materials more especially viscous materials requiring a high level of hygiene in handling.
2. Description of Prior Art
A variety of pneumatically operated double acting pumps are available having the capability of pumping fluent and viscous liquids. Usually, such pumps have a drive piston reciprocable by means of pneumatic pressure in a drive piston chamber. Piston rods extend from the drive piston in opposite directions and carry pumping pistons in pumping chambers. When the drive piston moves in a first direction a first one of the pumping pistons retreats in the first pumping chamber to suck liquid into this chamber through an upstream non-return valve in a liquid conduit to an from the pumping chamber. During this movement the second one of the pumping pistons advances into the second piston chamber and forces liquid out of it through a downstream non-return valve an a liquid conduit to this second pumping chamber. When the drive piston moves in the other direction liquid is forced from the first pumping chamber and sucked into the second pumping chamber.
Many variables of such pumps are known and exemplary pumps are disclosed in:
______________________________________ U.S. Pat. No. 3,450,055 Issued: June 17, 1969 To: England U.S. Pat. No. 3,776,665 Issued: December 4, 1973 To: Dalton U.S. Pat. No. 3,861,166 Issued: January 21, 1975 To: Goldsberry U.S. Pat. No. 4,730,991 issued: March 15, 1988 To: Handfield U.S. Pat. No. 5,094,596 issued: March 10, 1992 To: Erwin U.S. Pat. No. 5,324,175 issued: June 28, 1994 To: Sorenson ______________________________________
The above listed U.S. patents are exemplary of various double acting pumps. They also show the wide variety of uses to which such pumps may be put.
Pumping of viscous liquids in the food industry is not among potential uses because pumps for viscous liquids are subject to stringent hygiene controls and have provided especial difficulties in design. Any contamination of such product, for example, a food product, is unacceptable and frequently subject to Government regulations. Pumps used for this purpose must be frequently stripped down for cleaning. Replacement of pump parts may be more frequent than is strictly necessary since it is of paramount importance that no contamination reach the product being pumped. Thus seals and valves may be replaced well before the time they may expect to fail.
As a result, pumping food products is an unduly expensive operation due to the time spent in cleaning and servicing pumps and in the cost of installing replacement parts before it may be strictly necessary.
The present inventors have addressed the problem of providing a pump for viscous food products or for other liquids for which hygiene is of prime importance. The inventors have tried to devise a pump which may be cleaned in place, ie. without disassembly, by pumping cleaning fluid through it. They have tried to devise a pump of modular construction for quick and easy assembly and disassembly when necessary. They have also tried to devise a pump in which superfluous part replacement in the interest of avoiding potential contamination is not necessary. Thus they have tried to devise a pump in which it is immediately apparent when a seal fails and, moreover, failure of a seal does not lead to a contamination of a product.